Online shopping is all about trust and security. SSL certificates protect a web site from fraudulent activity, securing that the server which is sending the certificate information to the browser is the right server, and it does not allows the data interception. Every data is encrypted, whether it is incoming or outgoing; no third party (other than the browser and the server) not able to read data.

In fact, Secure Socket Layer (SSL) is the security layers that work for the encryption and authentication between the server and the browser where information or data travels on an insecure network via Internet. SSL encrypts data by using Asymmetric cryptography for key exchange, symmetric for privacy, and message authentication code for message integrity.
The site secured with SSL certificate start with https (hyper text transfer protocol secured by SSL) secured in the address bar of the browser, whereas the site which is not secured by SSL certificate start with http (hyper text transfer protocol).

In brief:

While using the sites that require sensitive information like, Ecommerce, Banking or payment transfer services like PayPal, you will see in the address bar “http” is replaced by “https”, this inclusion of “s” is due to the use of  cryptographic protocol i.e. SSL certificate. You can also see small padlock in the status bar. While, processing your confidential information, you’ll get a strong confidence that your information is passing securely over the Internet.

When browser requests a secure page, the browser sends a public key (used for encryption of data) and certificate, after checking: certificate is coming from a trusted party, certificate is valid or not, and its relationship with the site from which it is coming.